1. Field of the Invention
The present invention relates to a postprocessing apparatus attached to an image forming apparatus such as a printer and a copying machine, and an image forming apparatus and an image forming system including the postprocessing apparatus, and in particular, to a postprocessing apparatus that performs sheet bundling and aligning processing, and an image forming apparatus and an image forming system including the postprocessing apparatus.
2. Description of the Related Art
Already known is a finisher as a postprocessing apparatus that once accumulates sheets output from a copying machine or a printer in a stacking tray, aligns them, and performs binding processing thereon with, for example, a stapler using metal staples. Among such finishers, one capable of binding 50 sheets is the mainstream.
Thus, the conventional postprocessing apparatus binds a relatively large number of sheets. When aligning a sheet bundle, the postprocessing apparatus aligns a large number of sheets collectively through a width direction aligning unit such as a jogger. Such a conventional postprocessing apparatus requires space for the aligning unit for aligning a sheet bundle and an aligning unit configuration (a drive source) for aligning. For this reason, in most cases, the configuration of the conventional postprocessing apparatus cannot be simplified, and its size is nearly the same as that of a copying machine or a printer, leading to problems of cost increase, space management, and increased consumption of resources.
As one of such conventional postprocessing apparatuses, for example, Japanese Patent No. 4307429 discloses a sheet processing apparatus that can reduce the time for sheet aligning operation by an aligning unit. Disclosed therein is a technology that, using the aligning unit that stacks and aligns a sheet bundle in a sheet stacking unit, a shift conveying unit that is provided at the upstream side of the sheet stacking unit, and a detector that detects the width direction position of a sheet, shifts the sheet to a predetermined position through the shift conveying unit when the sheet is conveyed to the stacking unit and moves the aligning unit provided on the stacking unit to a vicinity of the predetermined position before the sheet is conveyed to the stacking unit.
In the technology disclosed in Japanese Patent No. 4307429, a sheet is shifted to the predetermined position through a shift roller and a width direction detector (a lateral registration detector) and is conveyed to the postprocessing apparatus. However, because the postprocessing apparatus has the width direction detector installed, the postprocessing apparatus cannot be simplified and thus problems of cost increase, space management, and increased consumption of resources cannot be solved.
The typical number of sheets bound in an office is as small as about five. When such a small number of sheets of about five are subjected to width direction aligning processing at the upstream side of the postprocessing apparatus and conveyed to the postprocessing apparatus, a large width direction deviation is less likely to occur as compared to 50-sheet binding, and only a small width direction deviation occurs.
Thus, because only a small deviation in the width direction occurs in the width direction aligning processing by the postprocessing apparatus for a small number of sheets, it is considered that eliminating the width direction aligning unit in the postprocessing unit can simplify the configuration of the postprocessing apparatus, reduce costs, save space, and further minimize the amount of width direction deviation of a sheet bundle.
An object of the present invention is, in view of the fact that the typical number of sheets bound in an office is as small as about five, to provide a postprocessing apparatus, and an image forming apparatus and an image forming system including the postprocessing apparatus that can simplify its configuration, reduce costs, save space, and further minimize the amount of width direction deviation of a sheet bundle by eliminating the width direction aligning unit in the postprocessing unit.